In printing processes such as Phase Change ink printing (“PC”) and Electrostatic toner Printing (“EP”) there typically exists a point in the process where pressure is applied to marking or printing substances, thereby pressing those marking or printing substances onto a substrate, which marking or printing substances then form a visual image. The marking substance in PC is typically a wax-based ink while the marking substance in EP is typically toner particles. The substrate in both PC and EP is typically paper. The pressure is typically formed between the “nip” of two rollers.
The permanent fixing or “fusing” of the marking or printing substances onto the substrate includes a warming process of the marking substances prior to, or upon their reaching the nip point. The warming process allows the wax or toner to become flowable and tacky. When the warmed marking or printing substances and the substrate reach the nip point, the nip pressure causes the wax or toner to flow into the fibers or pores of the paper. When the wax or toner cools, solidification of the wax or toner occurs thus causing the wax or toner to be bonded firmly to the paper.
The methods of thermally fusing wax or toner onto the paper inherently include some drawbacks. One such drawback of these fuser systems is that since the wax or toner particles are tackified by heat, part of the heated wax or toner particles forming the image are often inadvertently retained by the fuser roller rather than penetrating the paper's surface. This tackified wax or toner often sticks to the surface of the fuser roller and then gets deposited onto the following paper or onto the mating pressure roller. This unintended depositing of wax or toner onto the following paper is known as “offsetting”. Offsetting is an undesirable occurrence, which lowers the sharpness and quality of the immediate print and also contaminates the following prints with offset wax or toner.
To alleviate the wax or toner-offsetting problem, it is common practice to utilize release agents such as silicone oils, which are applied to the fuser roll surface and which act as wax or toner release agents. These wax or toner release agents possess a relatively low surface energy and are suitable for use in the fuser roll environment. In practice, a thin layer of silicone oil is applied to the surface of the fuser roll to form an interface between the fuser roll surface and the wax or toner particles. Thus, a low surface energy, easily parted layer is presented to the wax or toners that pass through the nip. This low surface energy layer of release agent thereby prevents wax or toner from adhering to the fuser roll surface.
Numerous systems have been used to deliver wax or toner release agents to the fuser roll. These systems sometimes incorporate a textile as the release agent fluid holding and delivery medium. Such textiles also serve an additional role in that they are utilized as a fuser roller cleaning mechanism. With each rotation of the fuser roller, there may be some non-released wax or toner particles remaining on the surface of the fuser roller. These non-released wax or toner particles are captured in the interstices of the textile fibers used to deliver the release agents to the fuser roll.
Some of the release agent delivery textiles, which are more commonly used in printing machines, are known as non-woven textiles. Some of the more commonly used non-woven textiles are known as hydroentangled non-woven textiles, needle felts, thermal bonds, and spun bonds. Many of the non-woven textiles used in printing machines are typically made of fibers with some content of polyesters, nylons, amides, aramids, imides, polyphenylene sulfide (PPS), PTFE, and/or viscose rayons. The textiles are typically impregnated with a silicone oil such as those sold by the Dow Corning Corporation. Many of these silicone oil impregnated textiles are manufactured at BMP America Incorporated located in Medina, N.Y. or at BMP Europe Limited located in Accrington, Lancashire, United Kingdom.
Although these oil impregnated non-woven textiles meet a number of application requirements, many applications demand still higher oil holding capabilities with low oil leak rates. In an effort directed to providing a printer which is as small as feasible, and thus having an oil delivery system which is as small as possible, every step towards reducing the size of the oil delivery system is critical in today's market. Certain oil holding issues still exist with the presently used textile materials. Under many conditions, current textile materials leak oil when saturated to high levels. These oil leaks are very undesirable and can decrease print quality because they can form oil blotches. They can also decrease the expected oil delivery life of the textile roller.
Every step towards increasing an oil delivery roller's oil holding capacity is a step towards increased oil delivery life while at the same time not sacrificing print quality.